<!DOCTYPE html>
<style>
td { border: 1px solid black; padding: 5px; }
table { border-spacing: 0; }
</style>
<div style="columns: 2">
  <table>
    <tr><td>
      <table>
        <tr><td>Inner</td></tr>
        <tr><td style="height: 100px"></td></tr>
      </table>
    </td></tr>
    <tr><td style="height: 400px"></td></tr>
    <tr><td>
      <table>
        <tr><td>Inner</td></tr>
        <tr><td style="height: 100px"></td></tr>
      </table>
    </td></tr>
    <tr><td style="height: 400px"></td></tr>
  </table>
</div>
